1. Field of the Invention
The present invention relates to an electron emitting device, an electron source, an image display device, and methods of manufacturing these devices.
2. Description of the Related Art
Conventional electron emitting devices are roughly of two types, including thermionic-cathode electron-emitting devices, and cold-cathode electron-emitting devices. Example of cold-cathode electron-emitting devices include a field emission type (referred to as xe2x80x9cFE typexe2x80x9d hereinafter), a metal/insulator/metal type (referred to as xe2x80x9cMIM typexe2x80x9d hereinafter), a surface conduction type, and the like, types of electron-emitting devices.
Known examples of FE type devices are disclosed in M. P. Dyke and W. W. Dolan, xe2x80x9cField Emissionxe2x80x9d, Advance in Electron Physics, 8, 89 (1956), C. A. Spindt, xe2x80x9cPhysical Properties of Thin-Film Field Emission Cathodes with Molybdenum Conesxe2x80x9d, J. Appl. Phys., 47, 5248 (1976), and Japanese Patent Laid-Open No. 3-46729.
Known examples of MIM type devices are disclosed in C. A. Mead, xe2x80x9cOperation of Tunnel-Emission Devicesxe2x80x9d, J. Apply. Phys., 32, 646 (1961), etc.
Examples of surface conduction electron-emitting devices are disclosed in M. I. Elinson, Radio Eng. Electron Phys., 10, 1290 (1965), Japanese Patent Laid-Open Nos. 7-235255, 8-102247, 8-273523, 9-102267, and 2000-231872, and Japanese Patent Application Nos. 2836015 and 2903295.
A surface conduction type of electron-emitting device uses the phenomenon that an electric current is caused to flow through a small-area thin film formed on a substrate in parallel with the film plane to emit electrons. As the surface conduction type of electron-emitting device, a device comprising a SnO2 thin film by Elinson, a device comprising an Au thin film (G. Dittmer: xe2x80x9cThin Solid Filmsxe2x80x9d, 9, 317 (1972)), a device comprising an In2O3/SnO2 thin film (M. Hartwell and C. G. Fonstad: xe2x80x9cIEEE Trans. EDConf.xe2x80x9d 519 (1975)), and a device comprising a carbon thin film (Hisashi Araki, et al: xe2x80x9cShinkuxe2x80x9d (Vacuum), Vol. 26, No. 1, p. 22 (1983)) are known.
An electron source substrate comprising a plurality of the above-described electron-emitting devices can be combined with an image forming member comprising a fluorescent material or the like to obtain an image forming apparatus.
However, in the surface conduction type of electron-emitting devices, stable electron emission performance and electron emission efficiency are not necessarily obtained. Therefore, at present, it can be difficult to provide an image forming apparatus having high accuracy and excellent operation stability by using surface conduction type electron-emitting devices.
Therefore, as disclosed in Japanese Patent Laid-Open Nos. 7-235255, 8-264112, and 8-321254, a device subjected to a xe2x80x9cforming stepxe2x80x9d may be subjected to a treatment called an xe2x80x9cactivation stepxe2x80x9d. The xe2x80x9cactivation stepxe2x80x9d represents a step of significantly changing a device current If and an emission current Ie.
Like the xe2x80x9cforming stepxe2x80x9d, the xe2x80x9cactivation stepxe2x80x9d can be performed by repeatedly applying a pulse voltage to the device in an atmosphere containing an organic material. In this step, carbon or a carbon compound is deposited in the gaps and near the gaps formed in the xe2x80x9cforming stepxe2x80x9d from the organic material present in the atmosphere. Consequently, the device current If and the emission current Ie are significantly changed to obtain higher electron emission performance. Furthermore, Japanese Patent Laid-Open No. 8-321254 discloses another method for improving the electron emission performance by a step different from the xe2x80x9cactivation stepxe2x80x9d disclosed in the above publications.
FIGS. 40A and 40B schematically show the general construction of a surface conduction type of electron-emitting device formed by the xe2x80x9cactivation stepxe2x80x9d disclosed in the above publications. FIGS. 40A and 40B are respectively a plan view and a sectional view of the electron-emitting device disclosed in the above publications.
In FIGS. 40A and 40B, reference numeral 131 denotes a substrate, reference numerals 132 and 133 denote a pair of electrodes (device electrodes), reference numeral 134 denotes a conductive film, reference numeral 135 (FIG. 40B) denotes a second gap, reference numeral 136 denotes a carbon film, and reference numeral 137 denotes a first gap.
FIG. 41 consisting of FIGS. 41A to 41D schematically shows an example of a process for forming an electron emitting device having the structure shown in FIGS. 40A and 40B.
First, the pair of electrodes 132 and 133 is formed on the substrate 131 (FIG. 41A).
Then, the conductive film 134 is formed for connecting the electrodes 132 and 133 (FIG. 41B).
Then, in a xe2x80x9cforming stepxe2x80x9d, a current is passed between the electrodes 132 and 133 to form the second gap 135 in the conductive film 134 (FIG. 41C).
Furthermore, in an xe2x80x9cactivation stepxe2x80x9d, a voltage is applied across the electrodes 132 and 133 in a carbon compound atmosphere to form the carbon film 136 within the gap 135 on the substrate 131 and on the conductive film 134 near the gap 135, to form the electron-emitting device (FIG. 41D).
On the other hand, Japanese Patent Laid-Open No. 9-237571 discloses a method of manufacturing an electron-emitting device. The method comprises a step of coating an organic material such as a thermosetting resin, or the like on a conductive film and a step of carbonizing the coating, instead of the xe2x80x9cactivation stepxe2x80x9d in which a pulse voltage is repeatedly applied between electrodes in an atmosphere containing an organic material to deposit carbon and/or a carbon compound on a device.
However, conventional devices have the following two main problems:
1) It is not necessarily easy to form a conductive film with a high accuracy in the films thickness and quality, thereby deteriorating uniformity in forming many electron-emitting devices in a flat panel display.
2) In order to form a narrow gap having good electron emission performance, many additional steps need to be performed such as a step of forming an atmosphere containing an organic material, a step of precisely forming a polymer film on a conductive film, etc., thereby complicating control of each of the steps.
Furthermore, in an image forming apparatus comprising plural electron-emitting devices, the electron emission performances of the electron-emitting devices must be made uniform to provide for a stable display. However, the conventional surface conduction type of electron-emitting devices have the following problems:
In the surface conduction type of electron-emitting device, an electron emission portion is formed by the xe2x80x9cforming stepxe2x80x9d (and the xe2x80x9cactivation stepxe2x80x9d), but the position of the electron emission portion varies according to various circumstances during formation.
However, in an electron source comprising a plurality of electron-emitting devices respectively having the electron emission portions formed at different positions, when a voltage with the same polarity is applied to each of the devices, significant non-uniformity occurs in the amounts of the electrons emitted. In some cases, an image forming apparatus using such an electron source causes non-uniformity in brightness.
Therefore, it is preferred to use electron-emitting devices comprising an electron emission section formed at predetermined positions. However, the formation position of a conventional electron emission portion of a conventional electron-emitting device cannot be sufficiently easily controlled.
In the conventional device, as shown in FIG. 41D, in addition to the xe2x80x9cforming stepxe2x80x9d, the xe2x80x9cactivation stepxe2x80x9d is further performed to form the carbon film 136 composed of carbon or a carbon compound and having the first narrower gap 137 in the second gap 135 formed by the xe2x80x9cforming stepxe2x80x9d, to achieve good electron emission performance.
However, a method of manufacturing an image forming apparatus using the conventional electron-emitting devices has the following problems:
Each of the xe2x80x9cforming stepxe2x80x9d and the xe2x80x9cactivation stepxe2x80x9d comprises many additional steps such as repeated current supplying steps, a step of forming a preferred atmosphere in each step, etc., thereby complicating control of each of the steps.
When the electron-emitting devices are used for an image forming apparatus such as a display or the like, a further improvement in the electron emission properties is desired for decreasing the power consumption of the apparatus.
Accordingly, the present invention has been achieved for solving the above problems, and it is an object of the present invention to provide a method of manufacturing an electron emitting device, a method of manufacturing an electron source, and a method of manufacturing an image forming apparatus, which are capable of simplifying a process for manufacturing an electron-emitting device, and of improving electron emission properties.
The present invention has been achieved as a result of extensive research for solving the above problems, and constructions of devices according to the present invention are as follows.
In a first aspect of the present invention, an electron-emitting device comprises:
first and second electrodes (first and second electroconductive films) disposed with a space therebetween on a surface of a substrate;
a carbon film disposed between the first and second electrodes on the surface of the substrate, and connected to the second electrode; and
a gap defined between the first electrode and the carbon film connected to the second electrode;
wherein within the gap, the space between a surface of the carbon film and a surface of the first electrode at an upper position apart from the surface of the substrate is smaller than that at the surface of the substrate, and the surface of the first electrode is partially exposed in the gap.
The electron-emitting device further comprises another carbon film disposed on the first electrode. In this embodiment, an interface between the first electrode and the another carbon film is exposed in the gap. Also in this case, in a plane which is substantially perpendicular to the surface of the substrate, and which passes through the first and second electrodes, the height of the another carbon film on the first electrode from the surface of the substrate is larger than the height of the carbon film connected to the second electrode relative to the surface of the substrate. That is, a distance between an upper surface of the another carbon film from an upper surface of the substrate is greater than a distance between the upper surface of the substrate between the electrodes and an upper surface of the carbon film which is disposed between the electrodes.
Furthermore, the end surface of the carbon film connected to the second electrode faces the first electrode in at least a portion of the gap.
In another embodiment of the present invention, an electron-emitting device comprises first and second electrodes disposed on a surface of a substrate, and a carbon film having a gap and disposed between the first and second electrodes on the surface of the substrate so that one end covers a portion of the first electrode, and the other end covers a portion of the second electrode, wherein a part of a surface of the first electrode is exposed in the gap, and the width of the gap at an upper position apart from the surface of the substrate is smaller than that at the surface of the substrate.
In the electron-emitting device, the part of the surface of the carbon film faces the first electrodes in at least a portion of the gap. Furthermore, an interface between the first electrode and a portion of the carbon film positioned on the first electrode is exposed in the gap.
In a still another embodiment of the present invention, an electron-emitting device comprises first and second electrodes disposed with a space therebetween on a surface of a substrate, a carbon film disposed between the first and second electrodes on the surface of the substrate so that one end portion of the carbon film covers a portion of the second electrode, and a gap defined at least by the other end portion of the carbon film and the first electrode.
Furthermore, the distance between the other end portion of the carbon film and the first electrode at an upper position apart from the surface of the substrate is smaller than that at the surface of the substrate. Also, another the carbon film is disposed on the first electrode.
In a plane which is substantially perpendicular to the surface of the substrate, and which passes through the first and second electrodes, the height of the another carbon film on the first electrode from the surface of the substrate is larger than the height of the carbon film, which is disposed between the first and second electrodes on the surface of the substrate (to cover a portion of the second electrode) relative to the surface of the substrate. That is, a distance between an upper surface of the another carbon film from an upper surface of the substrate is greater than a distance between the upper surface of the substrate between the electrodes and an upper surface of the carbon film which is disposed between the electrodes.
Furthermore, in at least a portion of the gap, the carbon film connected to the second electrode faces the first electrode.
In a till further embodiment of the present invention, an electron-emitting device comprises first and second electrodes disposed on a surface of a substrate, and a carbon film having a gap and disposed between the first and second electrodes on the surface of the substrate so that one end of the film covers a portion of the first electrode, and the other end covers a portion of the second electrode, wherein at least part of a surface of the first electrode is exposed in the gap.
In the electron-emitting device according to this embodiment, the interface between the first electrode and a portion of the carbon film covering the first electrode is exposed in the gap.
In a further embodiment of the present invention, an electron-emitting device comprises first and second electrodes disposed on a surface of a substrate, and a carbon film disposed between the first and second electrodes on the surface of the substrate so that one end portion of the film covers a portion of the second electrode, wherein another end portion of the carbon film faces the first electrode with a space interposed therebetween.
Also, the other end portion of the carbon film is spaced apart from the surface of the substrate, and another carbon film which is disposed on the first electrode. Furthermore, in a plane which is substantially perpendicular to the surface of the substrate, and which passes through the first and second electrodes, the height of the another carbon film on the first electrode from the surface of the substrate is larger than the height of the carbon film, which is disposed between the first and second electrodes on the surface of the substrate (to cover a portion of the second electrode) relative to the surface of the substrate. That is, a distance between an upper surface of the another carbon film from an upper surface of the substrate is greater than a distance between the upper surface of the substrate between the electrodes and an upper surface of the carbon film which is disposed between the electrdoes.
Each of the above electron-emitting devices of the present invention is preferably further characterized in that at least a portion of the surface of the substrate, which is positioned within (adjacent) the gap, is concave (or includes a depressed or recessed portion), a plurality of electron emission sections (referred to as xe2x80x9celectron emission pointsxe2x80x9d or xe2x80x9celectron emission sitesxe2x80x9d) are disposed in the gap, that a voltage is applied across the first and second electrodes to exhibit an asymmetric electron emission property according to the direction of an electric field applied between the first and second electrodes, and a width of the gap, in a direction of which the first and second electrodes are facing, is 50 nm or less, preferably 10 nm or less, and more preferably 5 nm or less.
In a further aspect of the present invention, a method of manufacturing an electron-emitting device comprises the steps of:
forming a pair of electrodes and a polymer film for connecting the electrodes on a substrate;
decreasing a resistance of the polymer film; and
forming a gap in a film obtained by decreasing the resistance of the polymer film;
wherein in the step of forming the gap, a current is supplied, through the pair of electrodes, to the film obtained by decreasing the resistance of the polymer film so that the Joule heat generated near an end of one of the electrodes is hither than the Joule heat generated near an end of another one of the electrodes.
In a further aspect of the present invention, a method of manufacturing an electron-emitting device comprises the steps of:
forming a pair of electrodes and a polymer film for connecting the electrodes on a substrate so that a contact resistance between one of the electrodes and the polymer film is different from the contact resistance between another one of the electrodes and the polymer film;
decreasing a resistance of the polymer film; and
forming a gap in a film obtained by decreasing the resistance of the polymer film;
wherein the gap is formed by supplying a current, through the pair of electrodes, to the film obtained by decreasing the resistance of the polymer film.
In a further aspect of the present invention, a method of manufacturing an electron-emitting device comprises the steps of:
forming, on a substrate, a pair of electrodes and a polymer film for connecting the electrodes by covering a portion of each of the electrodes;
decreasing a resistance of the polymer film; and
forming a gap in a film obtained by decreasing the resistance of the polymer film;
wherein the polymer film is formed so that the step coverage of a portion partially covering one of the electrodes is different from the step coverage of a portion partially covering the other electrode; and
the gap is formed by supplying, through the pair of electrodes, a current to the film obtained by decreasing the resistance of the polymer film.
In a further aspect of the present invention, a method of manufacturing an electron-emitting device comprises the steps of:
forming a pair of electrodes and a polymer film for connecting the electrodes on a substrate so that a structural configuration of one of the electrodes and the polymer film is different from a structural configuration of another one of the electrodes and the polymer film;
decreasing a resistance of the polymer film; and
forming a gap in a film obtained by decreasing the resistance of the polymer film;
wherein the gap is formed by supplying, through the pair of electrodes, a current to the film obtained by decreasing the resistance of the polymer film.
In a further aspect of the present invention, a method of manufacturing an electron-emitting device comprises the steps of:
forming a pair of electrodes having different shapes, and a polymer film for connecting the electrodes on a substrate;
decreasing a resistance of the polymer film; and
forming a gap in a film obtained by decreasing the resistance of the polymer film;
wherein the gap is formed by supplying, through the pair of electrodes, a current to the film obtained by decreasing the resistance of the polymer film.
Each of the above methods of manufacturing the electron-emitting device according to the present invention is preferably characterized in that the pair of electrodes are formed in different sizes, the pair of electrodes are formed to different thicknesses, and the pair of electrodes are formed so that an angle formed by a side surface of one of the electrodes and the upper surface of the substrate is different from an angle formed by a side surface of another one of the electrodes and the upper surface of the substrate.
In a further aspect of the present invention, a method of manufacturing an electron-emitting device comprises the steps of:
forming a pair of electrodes comprising different materials, and a polymer film for connecting the electrodes on a substrate;
decreasing a resistance of the polymer film; and
forming a gap in a film obtained by decreasing the resistance of the polymer film;
wherein the gap is formed by supplying, through the pair of electrodes, a current to the film obtained by decreasing the resistance of the polymer film.
In a further aspect of the present invention, a method of manufacturing an electron-emitting device comprises the steps of:
forming a pair of electrodes having different surface energies on a substrate;
forming a polymer film for connecting the electrodes disposed on the substrate;
decreasing a resistance of the polymer film; and
forming a gap in a film obtained by decreasing the resistance of the polymer film;
wherein the polymer film for connecting the electrodes is formed by coating the substrate with a solution of a polymer constituting the polymer film or a solution of a precursor of the polymer, and then heating the substrate with the solution coated thereon, and
wherein the gap is formed by supplying, through the pair of electrodes, a current to the film obtained by decreasing the resistance of the polymer film.
In a further aspect of the present invention, a method of manufacturing an electron-emitting device comprises the steps of:
forming a pair of electrodes having different compositions on a substrate;
forming a polymer film for connecting the electrodes disposed on the substrate;
decreasing a resistance of the polymer film; and
forming a gap in a film obtained by decreasing the resistance of the polymer film;
wherein the polymer film for connecting the electrodes is formed by coating the substrate with a solution of a polymer constituting the polymer film or a solution of a precursor of the polymer, and then heating the substrate with the solution coated thereon, and
wherein the gap is formed by supplying, through the pair of electrodes, a current to the film obtained by decreasing the resistance of the polymer film.
Furthermore, each of the above methods of manufacturing the electron-emitting device of the present invention is preferably characterized in that the pair of electrodes is formed by using a pair of conductive members comprising substantially the same material, and adding a material different from the conductive members to at least one of the pair of conductive members, and that the pair of electrodes is formed by connecting at least one of a pair of conductive members comprising substantially the same material to a member comprising a material having a lower standard electrode potential than that of the material of the conductive members, and heating at least the member comprising a material having a lower standard electrode potential than that of the material of the conductive members.
In a further aspect of the present invention, a method of manufacturing an electron-emitting device comprises the steps of:
forming a pair of electrodes and a polymer film for connecting the electrodes on a substrate so that a connection length (connection interface) between one of the electrodes and the polymer film is different in length from a connection length (connection interface) between another one of the electrodes and the polymer film;
decreasing a resistance of the polymer film; and
forming a gap in a film obtained by decreasing the resistance of the polymer film;
wherein the gap is formed by supplying, through the pair of electrodes, a current to the film obtained by decreasing the resistance of the polymer film.
Furthermore, the above method of manufacturing the electron-emitting device of the present invention is preferably characterized in that the connection length represents the length of connection (i.e., the connection interface is) between the polymer film and an end of a corresponding one of the electrodes, and that the connection length represents the length of (i.e., the connection interface is) a portion of contact between the polymer film and at least one of the substrates and a corresponding one of the electrodes.
In a further aspect of the present invention, a method of manufacturing an electron-emitting device comprises the steps of:
forming a pair of electrodes and a polymer film for connecting the electrodes on a substrate;
decreasing a resistance of the polymer film so that the resistance of a portion the film near one of the electrodes is lower than the resistance of another portion of the film near the other electrode; and
supplying, through the pair of electrodes, a current to a film obtained by decreasing the resistance of the polymer film to form a gap in the film obtained by decreasing the resistance of the polymer film.
Furthermore, the method of manufacturing the electron-emitting device of the present invention is preferably characterized in that the xe2x80x9cresistance decreasing stepxe2x80x9d comprises the step of heating one of the electrodes to a temperature higher than the temperature of another one of the electrodes or the step of irradiating the polymer film with at least any of electrons, light and ions, the substrate comprises a light-transmitting material so that light is transmitted through the substrate to irradiate one of the electrodes with light, and the step of supplying a current to the film obtained by decreasing the resistance of the polymer film to form the gap in the film is performed at the same time as the xe2x80x9cresistance decreasing stepxe2x80x9d.
The preferred conditions of these methods of manufacturing the electron-emitting device of the present invention include the following conditions:
The pair of electrodes is formed in different sizes.
The pair of electrodes is formed in different thicknesses.
The pair of electrodes is formed so that the angle formed by a side surface of one of the electrodes and a plane of an upper surface of the substrate is different from an angle formed by a side surface of the other electrode and the plane of the upper surface of the substrate.
The pair of electrodes is formed by using a pair of conductive members comprising substantially the same material, and one of the members contains a material different from the conductive members.
The pair of electrodes is formed by connecting at leas one of a pair of conductive members comprising substantially the same material to a member comprising a material having a lower standard electrode potential than that of the material of the conductive members, and heating at least the member comprising the material having a lower standard electrode potential than that of the material of the conductive members.
In one embodiment of the invention, the connection length represents the length of connection (interface) between the polymer and each of the electrodes at an end of each electrode.
The connection length, in another embodiment of the invention, represents the length of a portion of contact (interface) between the polymer film, the substrate and a corresponding electrode.
The step of forming the polymer film is performed by coating a solution of a polymer constituting the polymer film or a solution of a precursor of the polymer by using an ink jet method.
The solution is applied to a position on the substrate deviating from the center of the space between the electrodes.
The step of decreasing the resistance of the polymer film is performed by irradiating the polymer film disposed between the electrodes with a particle beam or light.
According to one of the embodiment, the particle beam is an electron beam.
According to another embodiment, the particle beam is an ion beam.
The light preferably is a laser beam.
An electron source according to the present invention comprises a plurality of the electron-emitting devices of the present invention, which are disposed on a substrate.
A method of manufacturing an electron source according to the present invention comprises manufacturing a plurality of electron-emitting devices by any one of the above-described methods of manufacturing an electron-emitting device of the present invention.
An image display device according to the present invention comprises the electron source of the present invention, and a light emitting member.
A method of manufacturing an image display device, which comprises an electron source comprising a plurality of electron-emitting devices, and a light emitting member according to the present invention, comprises manufacturing the electron source by the method of manufacturing the electron source of the present invention.
In a further aspect of the present invention, an electron-emitting device comprises two electron-emitting devices arranged in parallel and each comprises a pair of electrodes, one of the electrodes being used as a common electrode, an electron source comprises a plurality of these electron-emitting devices disposed on a substrate, and an image display device comprises the electron source and a light emitting member.
In each of the electron-emitting devices of the present invention, a space serving as an electron emission section can be formed at a predetermined position, and thus the electron emission characteristics and reproducibility can be improved.
The manufacturing method of the present invention can be significantly simplified, as compared with a conventional manufacturing method requiring the step of forming a conductive film, the step of forming a gap in the conductive film, the step of forming an atmosphere containing an organic compound (or the step of forming a polymer film on the conductive film), the step of forming a carbon film by supplying a current to the conductive film, and forming a gap in the carbon film.
In the present invention, the gap can be selectively formed in the carbon film near one of the electrodes, thereby permitting the stable production of a uniform electron emitting portion.
The electron-emitting device manufactured according to the present invention has excellent heat resistance, thereby permitting an improvement in its electron emission properties, which can be limited by the performance of a conductive film in a conventional device.
The electron-emitting device manufactured according to the present invention has a high efficiency of electron emission, and thus the power consumption of the device can be decreased when the device is used for an image forming apparatus such as a display or the like.
Furthermore, in the electron-emitting device manufactured according to the present invention, an electron emitting portion can be uniformly formed with high controllability, thereby improving uniformity in a display screen, and suppressing variations in devices when the device is used for an image forming apparatus such as a display or the like.
In the electron-emitting device according to the present invention, electrical conductivity is significantly asymmetric with respect to the polarities of the applied voltage. Namely, when a positive voltage is applied to the electrode near the gap, the flowing current is 10 times as much as the current with the same voltage (about 20 V) with the reverse polarity.
This indicates that the voltage-current characteristic is a tunnel conduction type under a high electric field. When an anode electrode is disposed on a device, and the distance between the device and the anode electrode is, for example, 2 mm, an electron emission efficiency of as high as 1% or more can be obtained with an anode voltage of 1 kV. This electron emission efficiency is several times as high as that of a conventional surface conduction type of electron emitting device.
The reasons why an asymmetric electron emission property and a high electron emission efficiency can be obtained are not known completely at present. However, this is possibly related to the fact that electrons are emitted from an asymmetric electron emission section, and one conceivable reason is that when the potential of the electrode adjacent to the gap is set to be higher than that of the other electrode in driving, a larger number of electron emission points can be obtained.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.